I think I figured it out... Here is what I have noticed. When you check out a
doent an LCK file is created on your computer as well as on the server. This
is used for the check in/out feature of DW/Contribute. Most of you probably
already knew that part...

Anyways, I have found that if you delete the LCK file from the server without
removing it from your local machine Contribute refuses to edit the doent
associated with it.

Of course, this is just a theory and I am trying to prove it.